The present invention relates generally to medium-voltage vacuum contactors and in particular to control systems for controlling and synchronizing multiple vacuum contactors.
A vacuum contactor generally comprises three interrupters or vacuum bottles operated by an electromagnet assembly through a mechanical linkage. Such vacuum contactors are resistant to a variety of adverse atmospheric conditions and have relatively long electrical and mechanical lives. Each interrupter consists of two contacts enclosed in a ceramic housing or metal bellows. An upper contact is mounted to a fixed shaft and the lower contact is mounted to a moveable shaft. Each contactor is in communication with a control module adapted to open and close the contacts of the contactors. Medium voltage vacuum contactors are designed to operate in the 2400-7200 volt range and may be used with all types of Alternating Current (AC), loads including, for example, three-phase motors, transformers, power capacitors and resistive heating loads.
Vacuum contactors oftentimes include microprocessor “controllers” in communication therewith and configured to allow the contactors to be controlled, for example, from remote locations by digital signals sent along a control network. Typically, these control networks are low-level control networks such as, for example, DEVICENET, having a limited number of nodes being based on the Controller Area Network (CAN) standard. For this reason, communication between a control system and the vacuum contactor controllers is normally limited to simple on and off commands. The timing sequence may be controlled by a Programmable Logic Controller (PLC).
Control systems for electrical switching devices such as contactors are generally known in the art. For example, systems such as those disclosed in U.S. Pat. Nos. 5,506,485 to Mueller et al. and 5,610,579 to Early et al. disclose control systems for electrical switching devices. Typically, the control networks communicating between the PLC are low-level control networks such as DEVICENET providing simple interface circuitry but being able to connect only a limited number of nodes being based on the CAN standard (originally intended for automotive use). DEVICENET communication between a control system and the vacuum contactor controllers is suitable for simple on and off commands. However, the aforementioned systems are adapted for use with relatively low-voltage switching devices. Accordingly, a system for operating relatively higher voltage switching devices is desired.
In the control of medium voltage motors and the like it may be desirable to provide for high-speed synchronization of multiple vacuum contactors or other operations that require high speed communication. Such high speed communication could be possible through higher speed control networks such as CONTROLNET or ETHERNETIP, but these networks require considerable interface circuitry and sophisticated interconnecting media that would be prohibitively expensive on individual vacuum contactor controllers.